The invention concerns a mold for aluminothermic welding of beams and/or metal rails longitudinally aligned with each other, which includes several components in a rigid refractory material capable of being temporarily assembled around two transverse beam/rail ends to be welded.
Document FR 2 890 668 describes such a mold whereof the components together define a mold cavity, opening upwardly, arranged to receive, by casting, a welding metal in liquid state and surrounding the two ends, an interval arranged between them and a first zone of each rail, immediately next to the corresponding end, to communicate a determined form to the welding metal during its solidification, as well as two continuous core prints arranged to bear against a second zone of each rail immediately next to the first zone thereof, opposite the corresponding end relative to said first zone. In particular, document FR 2 890 668 describes, in one embodiment, that the components, made of bonded sand to facilitate their destruction after a single use, are primarily three in number, made up of:                two approximately identical upper halves of the mold, which constitute the specular image of each other relative to a median longitudinal plane common to the two rails to be assembled and which surround, from one respective side of these two rails, zones of the latter parts and of the interval formed between them which correspond to the top of the foot, the core, the bottom, the sides and the top of the head, and        a lower or bottom component, having the general shape of a plate that completes the two upper parts below the foot of the rails and of the corresponding zone of the interval formed between them.        
These three components are generally retained together, around rails to be assembled using a metal casing, itself reusable from one mold to the next. The mold cavity, open at the top, communicates in this direction, with a feed shaft whereof one upper end is partially obstructed using an attached stopper. Moreover, this upper end of the feed shaft leads into a pouring basin on which a crucible for aluminothermic welding is installed. Thus, when the welding metal in liquid state flows from the crucible, the jet of liquid welding metal crashes into the stopper partially obstructing the feed shaft then flows at reduced speed on either side of said stopper in the feed shaft to then gradually fill the mold cavity.
Although such a mold is satisfactory regarding the quality of the welding, it is far from optimal. Indeed, the mold, as previously described, only connects the liquid steel from the zone of the head with the liquid steel contained in the upper part of the channel via an opening disposed transversely (the resupply) whereof the reduced dimensions allow only a limited heat transfer from the channel toward the head; the heat reservoir constituted by the liquid steel being found in the upper part of the channel therefore only very slightly contributes to slowing the solidification speed of the welding in the zone of the head. Moreover, the stopper of the prior art serves to stop the jet, so that the latter does not directly hit the bottom component forming the bottom of the mold and thus accelerate its erosion. However, this has the major drawback of extending the filling time of the mold due to the decreased flow speed, which leads to greater heat losses and, in the end, to obtaining remelting of lesser quality of the rail ends due to convection of the liquid steel of the welding.
One aim of the invention is to provide a mold which, during use, makes it possible to obtain optimized and better quality welding. To that end, provided, according to the invention, is a mold for the aluminothermic welding of metal beams/rails including at least two essentially identical components in rigid refractory materials capable of being temporarily fitted opposite each other around two beam/rail ends to be welded, each of the components comprising:                a first lower part having a face defining a mold cavity including, toward the top, an upper opening and arranged to receive, by casting, welding metal in liquid state, the face being able to surround the ends at the level of a foot and a core of said beams/rails, and a recovery channel for gas and welding metal in liquid state leading downward in a lower zone of the mold cavity and having an opening toward the top and        a second upper part, adjacent and topping the first lower part, including a chamber communicating at the bottom with the upper opening of the mold cavity, open toward the top, arranged to receive, by casting, welding metal in liquid state and able to contain the ends at the level of a head of said beams/rails, the chamber being a slow cooling chamber forming a non-compartmentalized volume in which the opening of the channel leads and bounded by an external wall of each of the components of the mold and by a lower opening able to be situated under the head.        
Thus, the fact that the chamber is a slow cooling chamber able to receive the head of the beams/rails to be welded and forming a non-compartmentalized volume bounded by the external walls of each of the components makes it possible, on one hand, for the jet of melt of welding metal in liquid state coming from the crucible to go directly and quickly into the mold cavity, reducing the heat losses as much as possible and therefore ensuring better remelting of the beam/rail ends to be welded during filling of the mold cavity, and, on the other hand, makes it possible to have a significant mass of welding metal in liquid state situated around the head making it possible to obtain slower cooling and therefore to increase the quality of the welding at the upper part of the beam/rail. Because of this, this chamber functions opposite the pouring basin of the prior art. Thus, relative to the prior art previously described, the elimination of any wall between the upper part of the channel and the zone of the head makes it possible for this zone to then benefit from the heat stored in the upper part of the channel and makes it possible to obtain slow solidification of the steel in that location.
Advantageously, but optionally, the mold of the invention presents at least one of the following features:                the volume formed by the cooling chamber is a geometrically convex volume,        the face is essentially concave and includes an edge able to come into contact with a zone of the beam/rail in order to seal the mold cavity to the welding metal in liquid state, at the level of the foot and the core,        the cooling chamber has an opening bounded by a surface able to come into contact with a zone of the beam/rail in order to seal the cooling chamber to the welding metal in liquid state at the head,        each component of the mold includes a third part, adjacent to and topping the second upper part, comprising a spill basin able to receive casting means of a crucible for aluminothermic welding and situated in an extension of the upper opening of the cooling chamber via communication means of the spill basin with said cooling chamber;        the mold includes a third component made of rigid refractory material intended to be placed below the foot at the ends of each beam/rail and including an upper face defining a bottom of the mold cavity,        the upper face of the third component is essentially flat and is able to come into contact with a lower face of the foot,        the rigid refractory material of the third component is more refractory than the refractory material of the first two components,        the rigid refractory material of the third piece is made up primarily of alumina; and,        the rigid refractory material is a bonded sand.        